1. Field of Invention
The present invention relates to an electrostatic recording apparatus. More specifically, the present invention relates to an electrostatic recording apparatus, for example, such as an electrographic copying machine, which exposes an original copy by means of a mobile light source (scanning means), forming an image by means of this exposure on a paper.
2. Description of the Prior Art
One example of the electrographic copying machine being the background of the present invention is disclosed, for example, in the Japanese Patent Application Laid-Open No. 12944/1983 laid open on Aug. 2, 1983 and so on. In the conventional electrographic copying machine of this kind, the moving speed at returning motion of the mobile light source (hereinafter referred to as returning speed) is always constant. For this reason, so far a problem as described below has been present.
FIG. 1 and FIG. 2 are graphs showing one conventional example of the relationship between the moving speed and time. FIG. 1 shows a case where a paper of A4 size is used, and FIG. 2 shows a case where a paper of A3 size is used. Both FIG. 1(A) and FIG. 2(A) show the movement of the light source. Both FIG. 1(B) and FIG. 2(B) show the operation of a paper feeding part, and "Tp" represent the operating time, more specifically, the rotating time of a paper feeding roller (not illustrated), that is, the time during which the tip of the fed paper is in contact with the register roller as described later. In FIG. 1 and FIG. 2, "Vf1" and "Vf2" show the speed at forward going motion (hereinafter referred to as forward going speed) of a scanning means, that is, the mobile light source (not illustrated), and "Tf1" and "Tf2" show the forward going time of the light source responding to the paper size, respectively. Accordingly, when a paper of A4 size is used, the light source goes a distance equivalent to an area F1 expressed by "Vf1.times.Tf1". Similarly, when a paper of A3 size is used, the light source goes a distance represented by an area F2. Furthermore, " Vr1" and "Vr2" are the returning speeds of the mobile light source (not illustrated), respectively, and "Tr1" and "Tr2" are the returning times of the light source in respective cases. Accordingly, the light source returns a distance equivalent to an area R1 expressed by "Vr1.times.Tr1" in the case of A4 size, and returns a distance equivalent to an area R2 in the case of A3 size.
Since the foward going distance and the returning distance are equal, a relation to F1 (F2)=R1 (R2) holds. On the other hand, since the returning speeds Vr1 and Vr2 are constant, a relation of Vr1=Vr2 also holds.
As is apparent from these FIG. 1 and FIG. 2, when the paper of A4 size is used, a time of "Tf1+Tr1" is required for a sheet of paper, while when the paper of A3 size is used, a time of "Tf2+Tr2" is required for a sheet of paper. That is, in the above-mentioned example, when the forward going distance is long, a long returning time is required, and in reverse, when the forward going distance is short, the returning time becomes short, and therefore on the case where the paper of A3 size is used, a longer time is required in comparison with the case where the paper of A4 size is used.
FIG. 3 and FIG. 4 are graphs showing other conventional examples of relationship between the moving speed and time of the light source. FIG. 3 shows a case where the paper of A3 size is used, and FIG. 4 shows a case where the paper of A4 size is used. In these examples as shown in FIG. 3 and FIG. 4, the returning speeds Vr3 and Vr4 of the light source are made higher respectively in comparison with the returning speeds Vr1 and Vr1 as shown in FIG. 1, and a relation of Vr3=Vr4&gt;Vr1=Vr2 holds. As is shown in FIG. 3, in this conventional example, the returning speed of the light source is set so that the returning time of the light source Tr3 agrees nearly with the paper feeding time Tp when the paper of A3 size is used. On the other hand, since Vr3=Vr4, when the paper of A4 size is used, as shown in FIG. 4, a waiting time Ts expressed by "Tp-Tr4" is produced. This is because, in the case of the A4 size, the paper feeding operation is not completed yet at the time when returning motion of the light source has been completed.
Thus, in the examples as shown in FIG. 1 and FIG. 2, a longer time is required, thereby the efficiency being worse in the case where a large-sized paper is used.
Furthermore, in the examples as shown in FIG. 3 and FIG. 4, the waiting time Ts is produced and the efficiency is not good in the case where a small-sized paper is used. On the other hand, in order to elongate the life of the machine by reducing the vibration thereof, it is desirable that the moving speed of the scanning means, that is, the light source is as low as possible. In this case, however, as shown in FIG. 1 and FIG. 2, too much time is required, and accordingly, as shown in FIG. 3 and FIG. 4, the returning speed is made higher. However, if the waiting time Ts is produced by increasing the returning speed, the mechanical shock should be rather minimized by suppressing the returning speed by the amount equivalent to this waiting time.
Thus, the conventional electrostatic recording apparatuses for example, the electrographic copying machine has not been able to cope with the above-mentioned deficiency because the returning speed is always constant.